1. Field of the Invention
This invention relates to the generation of gas, and more particularly to apparatus for variably generating a gas used for inflating purposes. Such apparatus is especially adapted for use with motor vehicle passive restraint systems wherein, upon impact of the vehicle, a bag is rapidly inflated by the gas to protect passengers or other mobile objects of the vehicle.
2. Description of the Prior Art
In the gas generating apparatus conventionally used for inflation purposes, a gas developed by combustion of a gas generating material is directed through a conduit into an inflatable device. The gas generating material burns during a constant time interval. As a result, the time interval during which the inflatable device is filled with the generated gas remains relatively constant. For certain inflation applications, such as the inflation of air bags used in motor vehicle passive restraint systems, it is desirable to variably control the inflation time interval. However, in gas generating apparatus of the type described, the cross-sectional area of the conduit and the burn time for a fixed quantity of gas generating material have been considered constant parameters. Thus, in order to variably control the inflation time interval, it has previously been necessary either to employ a hybrid system wherein a pressurized gas is variably admixed with gas generating from a fixed amount of gas generatng material, or to employ inflation systems capable of providing a variable amount of generated gas.
In use of the hybrid system, damage to the inflatable device can occur if the pressure and temperature of the hybrid gas are not carefully controlled. Unless the generated gas is cooled by contact with a sufficient amount of the pressurized gas, it may be hot enough to damage the inflatable device. In order to safely regulate the pressure and temperature of the hybrid gas, a system of relatively complex and expensive electromechanical components has previously been required. Inflation systems which vary the amount generated gas are even more expensive. As a result, the inflation time interval cannot be variably controlled in an economical manner.